So I have an interesting and confusing situation with my 2018 Lariat. I recently installed an AutoSpring 2" leveling kit and some 1.5" Bora wheel spacers, and installation went smoothly (at least as smoothly as a leveling kit install can be), but on the second day of driving the truck after the install I noticed a bit of a thump coming through the floor and steering wheel that seemed to be tied to wheel speed. At first I thought ****, I smoked an IWE, so I just pulled the wheels and tested the system. In 2WD with the engine on the half shafts still turn when spinning the rotor, so just to be sure I knew the issue I tested the vacuum on both IWE's, and they fully disengaged and held vacuum with 7 mmHg of negative pressure applied to the system. The half shafts also remained stationary when turning the rotors at this point. So I continued to work backward towards the solenoid, and noticed that with the truck on and in 2WD the solenoid was not sending vacuum to the IWE's, so they remained engaged and continued to spin with the half shafts. I swapped a known working solenoid from another 2018, and the issue persisted. No vacuum to the IWE's with truck running and in 2WD. So I bypassed the solenoid and pulled about 15 mmHg of vacuum on the main IWE vacuum line that connects to the top nipple of the solenoid, and the IWE's disengaged and held without issue. The half shafts remained stationary when turning the rotor, as they should. So it seems like there is some electrical/signal issue with the computer. Either no signal or the incorrect signal is being sent to the solenoid, causing it to do nothing even when the truck is put in 2WD or 4WD. Both solenoids exhibited the same issue on my truck, but worked when swapped into another 2018 F150. I tried disconnecting the battery, but no change. Am I missing something, or is there a module I can reset using Forscan that might fix this issue? I'm at a loss and have no issue taking it to the dealer, but they're closed today and I really need the truck for work. I'm just worried that having the hubs engaged full time and the TC open could cause an issue. Any advice is much appreciated!

 

Check all fuses? The solenoid is controlled by the Transfer Case Control Module. There is at least one other member here that had a bad one.
If all fuses are good, the TCCM would be my guess.
No, you won't hurt anything other than fuel mileage driving around with the IWEs locked, unless you were to shift into 4H/4L.

 

I'd also check all electrical connections to make sure something didn't get pulled loose or a wire broken when work was being done.

 

Checked all the "4x4" fuses listed in the manual (I believe 71 and 63), and both were in working order. I also did a visual inspection where I was working, and didn't see any damaged wires or loose connectors. Any idea where the wiring for the TCCM would be located in the engine bay/front wheel well areas? I was flying blind on that visual check, so it's possible I might have missed something. I've searched as many threads as I can find pertaining to my issue, and it doesn't seem to be a common one. It's very possible that the truck might have had this issue when I bought it, and I just now noticed it after being concerned about IWE issues after the level.

 

IIRC, the TCCM is mounted in the cab down below the glovebox. No reason for anyone to be doing anything in that area when doing your level.
If you have a DVOM, you could check the connector on the top of the solenoid. It has a switched ground, so, with truck running in 2WD, you should have power between both connectors. Have someone switch to 4A/4H or 4L, doesn't matter which and you should loose power. "If", you do loose power, your TCCM is giving a signal to open the vent and close off vacuum. "If", you do have power in 2WD, I'd probably replace the solenoid with an OEM part, not expensive, but use OEM, there's been a number of guys replacing with Dorman brand, and still have problem.

 

Thanks for the advice. I just checked the signal coming off the male connector that plugs into the solenoid. It read a pretty consistent 4.5ish volts when the truck is off, and when 4H is selected. When the truck is running in 2WD its sending roughly 12V. I compared those readings to my brother's 2018, and they are the same. So I have no idea what the hell is going on with this thing. If the signal is normal, and the problem persists even when I swapped in a new solenoid what could it be?

 

Did you stick both probes into the connector? Or just ground out somewhere else?

 

Both probes were in the connector

 

I'm at a loss now myself. The solenoid getting the signal like it is, should work. I assume you'll be getting it to the dealer, when you find out the cause, please post on here what's found. It may help someone else.
Sorry I can't figure it out either.

 

No worries, I appreciate your help either way. I've given up at this point, and will leave it up to the dealer to figure it out. I'll make sure to post an update once the dealer has taken a look at it. Thanks again.